Unhandled rejection from Cloud Function, but it runs sometimes

Question

I have some code that works sometimes, but sometimes it does not. When it does not run, I get this error: This is my code in Javascript: ``` exports.handleRequest = functions.database.ref('/Request/{usersUID}/{autoID}/{request}').onWrite(event => { let request = event.data.val(); let additionalRequest = event.data.key; let usersUID = event.params.usersUID; const generatedAutoID = event.params.autoID; event.data.adminRef.remove(); if (event.data.previous.exists()) { return; } if (!event.data.exists()) { return; } const functions = require('firebase-functions'); const admin = require('firebase-admin'); admin.initializeApp(functions.config().firebase); var db = admin.database(); var MasterAllCards = ["2_of_clubs", "2_of_spades", "2_of_diamonds", "2_of_hearts", "3_of_clubs", "3_of_spades", "3_of_diamonds", "3_of_hearts", "4_of_clubs", "4_of_spades", "4_of_diamonds", "4_of_hearts", "5_of_clubs", "5_of_spades", "5_of_diamonds", "5_of_hearts", "6_of_clubs", "6_of_spades", "6_of_diamonds", "6…

Accepted Answer

The intermittent failures may be the result of your not returning a `Promise` for the numerous asychronous Firebase operations your code performs. The Cloud Functions Guide explains:

It's important to manage the lifecycle of a function to ensure that it resolves properly... Also, you can make sure that the Cloud Functions instance running your function does not shut down before your function successfully reaches its terminating condition or state.

- Resolve functions that perform asynchronous processing by returning a JavaScript promise

Your code contains calls to `remove()`, `transaction()` and `update()`. Each of these completes asynchronously and returns a `Promise`. You need to chain or combine (see Promise.all()) the returned `Promises`, as needed, to ensure your function returns a `Promise` for any ongoing, asynchronous Firebase operation.

For example, to handle the two calls to `update()` at the end of the posted code:

```
const prom1 = pathSettingUpGame.update({
    ...
});

const prom2 = pathServer.update({
    ...
});

return Promise.all([prom1, prom2]);
```

There is also a Firebase video on returning Promises.

Unhandled rejection from Cloud Function, but it runs sometimes

Solution

Problem